Marc D chip, running extremely rich.

[hockeyguy68921]

The car has had a Marc D chip for the last few years and recently started to run rich with a possible misfire. At idle I could hear gas combusting in the exhaust along with a slight knock from the engine with a slight vibration. Decided to replace the OEM chip to see if it would make a difference, ran the car and it seemed to run even richer than before. I unplugged the MAF to see if it would make a difference to no avail. Reinstalled the Marc D chip, however, when I turn the car on it runs rich to the point where it will hardly climb revs and eventually cuts itself off. I'm not sure if it is misfiring worse than before causing it to cut off or if it's an issue with the injectors. If I can get it to run like it did before with the slight misfire/running rich I would be happy, but I'm not sure where I went wrong as I only reinstalled the OEM chip and then reinstalled the Marc D chip as it was before.

[MrBurgundy]

So, based on what you're saying, the OE chip and the MarkD chip makes no difference in how rich it runs? Pull the vacuum line off the fuel pressure regulator to see if its sucking gas through the intake.

You can actually test the MAF to make sure the signal is correct. You can search how to do that- all you'd need is a multi meter.

Next would be a bad oxygen sensor.

Start with the FPR

[hockeyguy68921]

Well after I reinstalled the Marc D chip, it began to run a lot worse. I understand that the fpr might be the cause of the car initially running rich before I changed the chips, but it would not result in the car's inability to run. Somehow just changing the chips back and forth has caused the car to run differently. I plan to leave the battery unplugged overnight and will try and start it tomorrow morning, however, I do not have much faith that it will fix the issue. I will look into testing the MAF, thanks.

[Digitalwave]

The issue does not sound chip-related. It probably runs differently because unplugging the ECU and changing the chip would reset any learning and trims that the ECU had stored.

Start with normal testing procedures to diagnose the problem.

It would help if you post more details such as which car/engine this is.

[Panici]

Have you checked ignition at each spark plug?

[hockeyguy68921]

The issue does not sound chip-related. It probably runs differently because unplugging the ECU and changing the chip would reset any learning and trims that the ECU had stored.

Start with normal testing procedures to diagnose the problem.

It would help if you post more details such as which car/engine this is.

The car is a 1988 325i. The car is mostly stock and the only upgraded components from the previous owner was a MAF, MarcD tune, and an Ireland engineering exhaust. Besides that, everything is pretty much stock. Within the last few years the distributor, rotor, spark plugs, plug wires have all been replaced. From what I know the injectors are still stock and I wouldn't be surprised if one or more of them is stuck open. I plan to get my hands on a torque wrench and check the spark plugs to see which one if any are gunked up. I want to try and get this car running back on its OEM chip as I believe the MarcD tune is not worth paying for 93. I appreciate your input.

[e30davie]

These chips and mafs are like a black box, who knows whats in them.. you are basically guessing.

If it were my car i wuld put it all back to stock electronics (maf, chip etc) and see how it goes and if its still shit make it run properly (maybe your blue temp sensor is stuffed). only once its running properly on OEM stuff, then add in the modded items one by one.

If you have a stuck open injector youll never get it running right, get them tested asap if you suspect.

Torque wrench for spark plugs? sheesh, i wouldnt. just do it by hand until its nice and snug, not tight.

[hockeyguy68921]

These chips and mafs are like a black box, who knows whats in them.. you are basically guessing.

If it were my car i wuld put it all back to stock electronics (maf, chip etc) and see how it goes and if its still shit make it run properly (maybe your blue temp sensor is stuffed). only once its running properly on OEM stuff, then add in the modded items one by one.

If you have a stuck open injector youll never get it running right, get them tested asap if you suspect.

Torque wrench for spark plugs? sheesh, i wouldnt. just do it by hand until its nice and snug, not tight.

I plan on just getting it back to stock and leaving it there, really don't have a lot of interest in getting power just want a good running car. It wasn't really the torque wrench I needed but I didn't have an extension to reach the plugs, just got one so I will take a look at them tomorrow.

What is a good way to test the injectors to see it's stuck open? I was planning on using a can of carb cleaner and alligator clips to test each injector and see if they are spraying correctly. If there is another way let me know.

I didn't think of the blue temp sensor, is there a way to test it without being able to run the car?

Thanks for the help.

[e30davie]

Id just remove the injectors and take them someone to get cleaned and checked. they will put new o-rings on them and new tips if they need it. youll Never have to worry about them again.

as for the blue sensor, there is resistance values you can test. give it a google or look in the readily available Bentley manual. at the very least i would remove it, clean it up so it has good contact with the ground and the sensor wire. if the ecu thinks the engine is always cold (sensor stuffed) it can be adding fuel all the time causing your always rich issue.

[moatilliatta]

You're looking in too deep. Restart with the basics. And the car probably has an AFM..

Plugs, Wires, Ign cap. Do cylinder balance test. Start here, no need to continue on your current path.

[Digitalwave]

I'd assumed you meant AFM when you said MAF. If the car has a MAF conversion, ditch it and put a stock AFM back in. The MAF conversions basically all suck, unless a standalone DME is done in conjunction. Motronic 1.3 was simply not meant to run with a MAF. It does not sound like a stuck injector to me, but like moatilliatta said, start with the basics.

[hockeyguy68921]

Hey guys, just took the spark plugs out and each of them are pretty coated in carbon. I didn't take any pictures of them but here is an image that I found that looks pretty much identical to the ones in my car. I put them back into the car and reinstalled the OEM chip to try and give the car a start which I took a video of. https://youtube.com/shorts/Fqk5kyPMGXs . As you can hear it barely fires on one cylinder very briefly before cutting off. My idea is that its a fueling problem but it's just odd that a few days ago it was able to run, although rich to the point I could smell fuel, and now it will barely turn over. I am not unsure if it is the fault of the injectors since the carbon fouling was uniform on each spark plug

Also from what I can tell the car does still have a stock AFM. I don't think the previous owner ever tinkered with the inner spring, but if it is something that you think I should look into I can open the plastic bit and take a look.

Also if the blue temp sensor was faulty, I wouldn't think that it would have an effect on the startup since it would still think the engine is cold which it is.

[hockeyguy68921]

Does anyone have any insight on why it will not turn over? Would the excessive carbon on the spark plugs lead to issues with it creating an arc, leading to failure to detonate? I'm really surprised the car fails to turn over since I have not changed any components besides the ECU chip.

[MrBurgundy]

That sounds like a bad fuel pump TBH. Running lean will sputter, pop and bang.

take the fuel hose off to the rail and crank it.

When the car won't start, you gotta get to the basics and start with a fuel pump test, spark test and based off the sound of it cranking, it has compression, so I'd say its safe to skip that part.

[hockeyguy68921]

That sounds like a bad fuel pump TBH. Running lean will sputter, pop and bang.

take the fuel hose off to the rail and crank it.

When the car won't start, you gotta get to the basics and start with a fuel pump test, spark test and based off the sound of it cranking, it has compression, so I'd say its safe to skip that part.

Yeah I have a feeling its spark, It recently had a walboro fuel pump conversion so I doubt its the pump. I didn't have anyone to crank it for me yesterday while I checked for spark but today I do so it will be the first thing I check.